The general objective in the treatment of gas streams from industrial and sewage plants is to remove from such gas streams odorous constituents, such as volatile organic compounds (VOCs) and volatile inorganic compounds (VICs). It is well known in the prior art to remove odors from waste gases in liquid-gas reactions through absorption utilizing spray towers systems and packed towers. In conventional spray tower systems, an aqueous solution containing one or more chemicals reactive toward an odorous contaminant is atomized to create liquid droplets which are dispersed into a gas stream. The atomized liquid droplets react with malodorous compounds to absorb odors and oxidation of such odors removes them from the gas stream. The reaction vessels are constructed to provide desired reaction times between the gas and the atomized aqueous/chemical fog, such reaction times typically ranging from about 5 to about 30 seconds or more for mist systems, and approximately 2 seconds for packed towers.
These and other traditional approaches have in common a relatively long contact time between gas and liquid, for mist scrubbers, and use a relatively large volume of liquid per volume of gas treated. Conventional spray and packed tower systems are inefficient with respect to the amount of chemical used. Moreover, conventional devices tend to be large and are expensive to construct and operate.
In other conventional liquid-gas absorption processes, packed tower systems are utilized to provide large surface areas for the liquid-gas reaction to occur. However, packings used in packed towers are often clogged by solid particulates and reaction products, negatively affecting the efficiency and overall function of such packed tower systems. Moreover, the size and expense of packed tower systems often precludes their use in many applications.
Problems in the treatment of sewage have also been encountered in the storage of sewage for extended periods of time. Among the problems, facultative bacteria present in sewage can react with sulfates in the absence of oxygen, thereby producing hydrogen sulfide, a malodorous poisonous gas, as well as other undesired odorous compounds. A combination of hydrogen sulfide gas with condensed water can form sulfuric acid which can cause deterioration of sewer pipes and sewer systems. Other undesirable compounds and gases may also form and need to be treated.
In conventional sewage systems, sewage is often held in various process apparatuses, such as a wet well, prior to treatment. Methods have been previously employed whereby chemicals are continuously fed into the wet well pump discharge line when the pump is operating or fed continually into the wet well. A continuous release system, however, may involve the undertreatment or overtreatment of sewage depending upon the time required for the wet well to fill to a predetermined level prior to evacuation. Alternatively, other systems treat malodorous sewage during the transport of such fluid from the wet well to other treatment containers. However, the sewage in the wet well prior to evacuation has the opportunity to ferment bacteria that produce undesired, odoriferous compounds.